This invention relates generally to rotary valve apparatus and, more particularly, to apparatus of this type that are adapted to handle materials at various temperatures while continuously maintaining an effective seal against the leakage of gases through the apparatus.
Rotary valve apparatus are used as air locking devices for transferring particulate solid materials between two regions having differing pressures, and as volumetric feeders. When the apparatus is functioning as an air locking device, it is desirable that changes in pressure between the two regions be held to a minimum since such pressure changes can constitute a hazard or create such deleterious effects as corrosion, contamination and erosion, or systematic loss of efficiency.
Typically, rotary valve apparatus consist of a cylinder housing having inlet and outlet openings for material passage and a rotating unit within the housing having a number of pockets for transferring material from the inlet to the outlet openings. The closer the clearance between the housing and the rotating unit can be held, the less leakage (pressure loss) there will be. The pockets have been formed by using vanes along an axial member in a sealing engagement with the walls of the cylindrical chamber. The tips of the vanes have been a point of attention in trying to alleviate the problem of leakage. The solutions have been varied, one being the employment of a metal strip across the vane biased by springs and/or a gas pressure applied to the metal strips. Another attempted solution employed the use of flexible vane blade members. The main problems encountered have been caused by particles becoming entrapped between the vane blade portion of the vane and the housing which causes bending or abrasion, and, therefore, leakages. In addition, those devices which employ a flexible blade member place a pressure constraint on the system. High system pressure may cause the flexible blade to excessively deform, providing a means for system pressure loss.
The devices used in the prior art attempt to accommodate varied operational temperatures by allowing for thermo-expansion, and by so doing, have sacrificed efficiency at off design parameters.
This invention minimizes the leakage problems and the destructive effects resulting from trapped particles between the vane blade and housing, yet maintains an effective seal at different operating temperatures, and system pressures.